Cutter inserts for drill bits for use in boring into the earth may comprise a layer of polycrystalline diamond (PCD) bonded to a cemented carbide substrate. Polycrystalline diamond (PCD) is an example of a superhard material (also called superabrasive material) comprising a mass of substantially inter-grown diamond grains, forming a skeletal mass defining interstices between the diamond grains. PCD material may comprise at least about 80 volume % of diamond and may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa and a temperature of at least about 1,200 degrees centigrade in the presence of a catalyst material for diamond, which is material that is capable of promoting direct inter-growth of diamond grains at a pressure and temperature at which diamond is thermodynamically more stable than graphite. Some catalyst materials for diamond may promote the conversion of diamond to graphite at ambient pressure, particularly at elevated temperatures. Examples of such catalyst materials are cobalt, iron, nickel and certain alloys including any of these. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. The interstices with PCD may be at least partly be filled with catalyst material for diamond.
PCD is extremely hard and abrasion resistant, which is the reason it is the preferred tool material in some of the most extreme machining and drilling conditions, and where high productivity is required. A disadvantage of PCD containing certain catalyst materials for diamond as a filler material may be its relatively poor thermal stability above about 400 degrees centigrade. The catalyst material may promote the degradation of the PCD at elevated temperature, particularly at temperatures greater than about 750 degrees centigrade, as may be experienced in manufacture and use of PCD compacts.
GB patent number 1 598 837 discloses removing metallic phase infiltrant material from a PCD compact comprising a PCD layer bonded to the cobalt cemented tungsten carbide layer by boiling in acid. Prior to immersion in the acid, epoxy resin was cast around the compact, leaving the surface of the diamond layer exposed by sanding away all of the plastic on the surface of the layer.
United States patent application publication number 20050115744 discloses a method of manufacture of a PCD element comprising a body integrally formed with a metallic substrate, the body comprising bonded diamond crystals and a catalysing material is also disclosed. The treatment is performed by treating the body to render a volume thereof substantially free of the catalysing material while permitting the catalysing material to remain in at least some of the remaining volume of the body and while permitting the substrate to remain substantially unaffected when treating the body.
United States patent application publication number 20080142276 discloses a method for making a thermally stable ultra-hard material compact construction comprising a body and a substrate. The method comprises the steps of: forming a thermally stable polycrystalline diamond body by removing a catalyst material therefrom; aligning complementary surface features positioned along interfacing surfaces of the body and substrate with one another so that they engage one another; and joining the body to the substrate.
United States patent application publication number 20090178855 discloses making thermally stable PCD (TSP). Firstly, a polycrystalline diamond layer is formed over a substrate at a non-uniform interface using known sintering methods. After sintering the PCD layer on the substrate, the substrate is removed so as to expose the non-uniform interface. The PCD layer is then leached as necessary to form the appropriate TSP layer.
United States patent application publication number 20080185189 discloses attaching a leached PCD compact to a substrate in a second HPHT (high pressure, high temperature) sintering step.
United States patent application publication number 2008230280 discloses a method for making PCD constructions by treating a polycrystalline diamond body to remove solvent catalyst material disposed within interstitial regions between the bonded together diamond crystals, and then replacing the solvent catalyst material with a replacement material.
United States patent application publication number 20100012390 discusses that where thermally stable PDC elements are produced by leaching out the cobalt or other binder-catalysing material, the leaching process also removes the cemented carbide substrate. In addition, because there is no integral substrate or other bondable surface, there are severe difficulties in mounting such material for use in operation. Subsequent joining of the leached PCD element to a tungsten carbide substrate in a high-pressure, high-temperature environment results in an abrupt transition between the diamond layer and the substrate, making the diamond layer susceptible to wholesale fracture at the interface at very low strains.